I'm using Filemaker 14 not 13, and Filemaker Go 14
If you close the database on the IPad and then open it, can you update the record? It may have something to do with your connection type. In the office and at home, I suspect you have a WiFi connection. In the field you are probably using a cell carrier to connect. You may have a weak connection.
For a number of clients who are doing this, I have set up a sync system, 360Works' Mirror Sync or SeedCode's GoZync.
Make sure you close the fmgo file before moving locations. Most users just shut their cover when finished. Highly recommend closing files when finished.